Experiments are proposed which should increase our knowledge regarding the mechanisms involved in the regulation of progesterone secretion from the corpus luteum by luteinizig hormone (LH). Since the initial action of LH involves binding to a receptor in the plasma membrane the factors which regulate the number of receptors will be ascertained. The endocrine factors involved in loss or stimulation of new receptors will be evaluated both in vivo and in vitro using Scatchard analysis to quantify unoccupied receptors and elution of the hormone from the membrane and quantitation by radioimmunoassay to quantify receptors occupied by LH. The LH-luteal receptor complex appears to mediate its stimulatory effect on steroidogenesis via activation of adenylate cyclase, elevation of protein kinase and direct activation of steroidogenic enzymes and synthesis of new protein. Biochemical experiments will be conducted to ascertain the details for each of these steps in the action of LH. Kinetically valid assays will be used to quantify the steroidogenic enzymes, adenylate cyclase and protein kinases following various biological and endocrine manipulations. Additional experiments will be performed to ascertain how the various precursors for progesterone secretion (i.e., cholesterol esters, cholesterol and pregnenolone) are compartmentalized within the cell and to elucidate the mechanisms involved in progesterone secretion.